This invention relates to an intake control valve for an internal combustion engine and more particularly to an improved method of operating such a control valve so as to optimize engine performance under a wide variety of conditions.
As is well known, many facets in the design and construction of internal combustion engines represent a compromise between maximum efficiency, maximum power and good running under widely varying conditions. The induction system is a prime example where such compromises may be required. When running at low speeds and low loads, it is desirable to induce a large turbulence to the charge that enters the combustion chamber so as to insure rapid flame propagation and full combustion. Although a wide variety of constructions and techniques have been employed for introducing such turbulence to the induction system, these turbulence inducing devices all substantially restrict the ability of the engine to breath under high speed, high load conditions.
There have, therefore, been proposed arrangements that incorporate a control valve in the induction passage which has the effect of not only changing the cross sectional area and, accordingly, the velocity of the charge entering the combustion chamber but additionally varying the direction in which the charge enters the chamber. Such devices can improve the efficiency of the engine at low and mid ranges without adversely affecting the high performance characteristics of the engine. Examples of such flow controlling induction systems may be found in the co-pending applications of Yoshiharu Osaka entitled "Tumble Control Valve For Intake Port", Ser. No. 834,604, filed Feb. 12, 1992 and "Intake Air Control System For The Engine", Ser. No. 893,111, filed Jun. 3, 1992, which applications are assigned to the Assignee hereof.
The constructions shown in those patent applications are extremely effective in providing good running over a wide variety of engine running characteristics. It has been found, however, that the performance of the engine both in the terms of exhaust emission control, fuel economy and engine output performance can vary significantly with the position of the control valve. Said another way, it has been found that the optimum position of the control valve for given running conditions varies with a number of parameters.
It is, therefore, a principal object to this invention to provide an improved induction control system for an engine.
It is a further object to this invention to provide an improved engine induction system incorporating a control valve and an improved arrangement for positioning the control valve.
In connection with the control of control valves of the type shown in the aforenoted patents, it has also been found that under certain ranges of engine running conditions there is an advantage in maintaining the control valve in either its flow restricting or its fully opened position, even though this condition may not be the optimum for the actual engine condition. By maintaining the control valve in one of its positions under a range of running operations, it has been found possible to improve fuel economy and/or performance depending upon other characteristics of the engine.
It is, therefore, a still further object to this invention to provide an improved induction system incorporating a control valve and a strategy for maintaining the control valve in one of its positions during a range of engine conditions.
With spark ignited engines, it is also a practice to vary the timing of firing of the spark plug in response to engine running conditions, most normally engine speed and/or load. For example, under low speed, low load conditions the spark is normally fired at an advanced condition so as to insure that full combustion can occur at the appropriate time. However, as the speed of the engine increases, the amount of spark advance is normally retarded from the low speed condition although the spark plug is always fired before top dead center. Of course, the optimum spark timing will vary depending upon a number of factors.
It has been further found that if conventional spark timing is employed in conjunction with an engine having an induction system control valve, then under some ranges of control valve operation the spark timing may not be optimum. For example, it has been the practiced, as noted above, to advance the spark timing when operating at low speed, low load conditions because of the low rate of flame propagation in the combustion chamber. However, when a control valve is employed for redirecting the charge and creating turbulence in the combustion chamber, then the conventional spark timing will not be appropriate.
It is, therefore, a still further object to this invention to provide an improved spark control arrangement for an engine having a control valve wherein the spark timing is varied in relation to the control valve position.
Although it may be possible, as previously noted, to determine the optimum position of the induction control valve for given running conditions, transient conditions present a different type of problem. For example, under high speed, high load conditions it is normally desirable to maintain the control valve in its opened position while under low speed, low load conditions it is desirable to maintain the control valve in its closed or flow controlling position. However, when decelerating from a high speed, high load condition due to rapid closure of the throttle valve or a sudden decrease in operator demand, then the throttle valve or operator throttle control will indicate a low speed, low load condition while the engine is still operating at high speed. Under such conditions, it has been desirable to maintain the control valve in its fully opened position even though the speed control position may indicate a different running condition.
It is, therefore, a still further object to this invention to provide an induction system having a control valve and improved strategies for operating to provide better performance under certain types of transient conditions.
In addition to the positioning of the control valve under extreme deceleration conditions, as aforenoted, it is also desirable to change the spark timing when the control valve is held in its fully opened position and independently of the other sensed engine conditions so as to improve fuel economy.
It is, therefore, a still further object to this invention to provide an improved spark control system for an engine having a control valve in its induction system and which control valve is held in one position in response to a sudden change in operator demand.
Another condition when the positioning of the control valve may be determined primarily by one engine condition other than those normally sensed, is when the engine is stopped. Normally when the engine is stopped, the throttle control will be positioned in a position that would call for the control valve also to be positioned in its flow restricting position. Depending upon the geometry of the induction system and the type of charge former employed, such closure of the control valve could trap residual condensed fuel in an upstream location in the induction system. This trapped fuel could give rise to certain problems when the engine is being restarted. On the other hand, there may be some types of engine configurations or some conditions when it is desirable to maintain the control valve in its closed position when the engine is shut off.
It is, therefore, a still further object to this invention to provide an improved arrangement for operating the control valve upon the stopping of the engine to place it in one of extreme positions and regardless of the other engine conditions which may be sensed.
As has already been noted, during starting of the engine and when operating at low speeds and low loads, it is desirable to position the control valve in a closed or flow restricting position so as improve turbulence and redirect the air flow in the combustion chamber. However, there may be some instances when even this is not desirable.
For example, if the engine is provided with a catalytic convertor or other type of device for treating the exhaust gases, it is desirable to insure that this exhaust treatment device is at its operating temperature or brought to that temperature quickly during cold starting and warm up. This is because catalytic convertors must be at their operating temperature before they become effective. Thus, under some cold start up conditions it may be desirable to promote other than the best combustion efficiency in the engine so that a fuel rich mixture may be delivered to the catalytic convertor so as to cause it to heat more rapidly.
It is, therefore, a still further object to this invention to provide an improved induction system and control device therefore that will assist in cold starting warm up.